Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology can use either thermal ink jet technology or piezoelectric technology. Even though they are more expensive to manufacture than thermal ink jets, piezoelectric ink jets are generally favored as they can use a wider variety of inks.
Piezoelectric ink jet printheads typically include a flexible diaphragm and an array of piezoelectric elements (i.e., transducers or PZT's) attached to the diaphragm. When a voltage is applied to a piezoelectric element, typically through electrical connection with an electrode electrically coupled to a voltage source, the piezoelectric element bends or deflects, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
Ink jet printheads can include a semiconductor die, for example a silicon die, a jet stack subassembly, a printhead subassembly, or another structure as a printing device, which is in fluid communication with the ink reservoir. The printing device is typically attached to the ink reservoir, or to an intervening interposer between the ink reservoir and the printing device, using a B-stage adhesive. Creating a fluid-tight seal between the printing device and the ink reservoir using a low-cost thermoset adhesive can be challenging. Seal failures and defects can include voiding of the adhesive between the printing device and the ink reservoir, thus resulting in a site where ink can leak into an undesired location. Another failure, squeeze-out, can result when the adhesive is forced laterally from between the printing device and the ink reservoir during bonding. Squeeze-out can result in either an ink leak between the printing device and the ink reservoir or an occlusion (blockage) by the adhesive within an opening such as an ink channel that is configured for the passage of ink. Further, proper placement of the adhesive is a concern, particularly with decreasing device dimensions. Also, bond line control (i.e., proper thickness of the adhesive as it is dispensed onto a surface) is a concern, as excessive adhesive contributes to squeeze-out, occluded openings, and adhesive voiding. These adhesive issues can negatively impact the fluid seal and cause the print device to fail through ink port plugging and external leaking. Defects related to adhesive can be more problematic for certain design implementations. For example, fine micro-sized fluidic features in the range of 50 to 100 microns or smaller located at the physical edges of their respective devices can be even more difficult to seal. In this case, obstacles such as lack of available bonding area and high risk of occlusions require new approaches for bonding.